Coded track circuit signaling system



June 6, 1944. T. J. JUDGE CODED TRACK CIRCUIT SIGNALING SYSTEM FilledAug. 24, 1942 gsheets-Sheet 1 BTE 212 l l l l l RF1-E QJ* ci@ ETE E Eontrol Office Appai'atus CTCLomrriuncaton Syste.

June' e, 1944. T, J, JUDGE 2,350,620

CQDED 'TRACK CIRCUIT SIGNALING SYSTEM 5H DI @if {IFI- BY g f3 mw June6., 1944. T. J. JUDGE `2,350,520

" conm TRACK cmcum smNALINe sYsTEM l Filed Aug. 24, 1942 9 sheets-sheet5 June 6, `1944. 1'. J. JUDGE CODED TRACK CIRCUIT SIGNALING SYSTEM ssheets-sheet 4 Filed Aug` 24, 1942 ATTORNEY June 6, 1944. r. J, JUDGE2,350,620

f CoDE'D TRACK CIRCUIT SIGNALINC sYsTEM Filed Aug'. 24, 1942 9sheets-sheet s maze-'21:19. ...J "gym l BY MM (,/LAZTTOIQEY l T. J..JUDGE CODED TRACK CIRCUIT SIGNALING SYSTEM June 6, 1944.

EiledAug. 24, 1942 9 sheets-sheet e FIGA.

. ATTORNEY June 6, 1944. r. J. JUDGE CODED TRACK CIVRCUVIT SIGNALINGSYSTEM Filed Aug. 24, 19'42 9 sheets-sheet '7 TTORNEY June 6, 1944. T.J. JUDGE com: TRACK cmcu'r SIGNALING sYsTEM Filed Aug. 24, 1942 9Sheets-Sheet 8 53 BEP E m021. E M vou Plum@ ATTORNEY `*lune 6, 1944. T.J. JUDGE CODED TRACK CIRCUIT SIGNALING' SYSTEM 9 sheets-Sheet 9 FiledAug. 24, 1942 ...9N :o wuvm. xus. E 0251.5 II .muon Humm E, VIAS@ E JV 7j wII EN r V T I f llmmpfwmw |Nv NTO ATTORNEY Patented June 6, 1944CODED TRACK CIRCUIT SIGNALING SYS TEM

Thomas J. Judge, Rochester, N. Y., assignor to General Railway SignalCompany, Rochester,

Application, August 24, 1942,. Serial No. 455,922

46 Claims.

This invention relates to coded track circuit signaling systems forrailroads, and it more particularly pertains to a system for singletrack railroads used in connection with centralized traiiic control.

According to the general organization of the system provided by thepresent invention, the automatic control of the signals in accordancewith tra-flic conditions is effected entirely through the track rails bycoded track circuit control, the only line wires required' being thoseassociated with the communication of controls from a control oilce tothe respective ends of the passing sidings generally known as fieldstations. Although the apparatus at the eld stations can be governed bydirect wire control from the control oflice, it is generally desirablefor the purpose of saving line wires that a suitable code communicationsystem be employed as is shown, for example, in the patent to Judge etal., No. 2,082,544, dated June l, 1937, or in the patent to Halles etal., No. 2,259,561, dated October 21, 1941.

One object of the present invention is to provide coded track circuitsin which driven code pulses are normally transmitted in oppositedirections at different intervals through each track section. Such adriven code is characterized by having its impulses transmitted inaccordance with the intermittent operation of coding'contacts and alsocalled oscillator contacts. 'I'he invention then provides that thecoding contactsv normally eiective at the opposite ends of each tracksection (or track circuit) operate at substantially differentpredetermined rates. This application of code pulses of di'iierent ratesat the opposite ends of a track section causes the pulses to combine ina manner to effect the intermittent operation of the track relays atboth ends of the section in accordance with what has been convenientlytermed a beat code. Although the code following track relay at each endof a section operates as a result of impulses transmitted from theopposite en'd of the section, such operation is not in exact conformanceto the operation of the coding contacts at that other end but is inaccordanceA with a modified or beat code whichv is used to detectoccupancy and provide a tumble-down circuit control as required for acentralized trafc control system for single track railroads. y n

Such an organization is considerably different than thoseY known in theprior art where a driven code is transmitted inl one direction through atrack section andan inverse codey is transmitted in the oppositeVdirection through that track section, because the transmission of aninverse code is wholly dependent upon the reception of the driven codeand is tranmitted during the 01T periods of such driven code. Thus, insuch an organization the cessation of the driven code also causes thecessation of the inverse code, while in the system of the presentinvention, the stopping of the transmitting means at one end of a tracksection merely allows the driven code at the other end to be transmittedwithout interference and received in accordance with the exact rate ofits coding contacts then effective.

Also, in such prior systems the driven code in a track section has arate' in accordance with the coding contacts at the transmitting end,while the inverse code takes the samerate as the driven code. But, whenthe present invention transmits driven codes in opposite directionsthrough a section, the result is beat codes which operate the trackrelays at both ends of the track section as above mentioned.

Another object of the present invention is to so control the codetransmitters at the opposite ends of a track section during normal beatcode transmission, that the impulses making up. the

,beat code are of substantial duration to causeV a positive operation ofthe track relays at both ends of that track section. `This isaccomplished in accordance with the present invention by controllingeach transmitter of a track section so that it cannot interrupt thereception of a pulse from the other end of that track section. Thus,once a transmitter has applied an impulse, such impulse `can beterminated only' by that transmitter, which provides that the impulsesof the beat codes are. usually of suflicient length to cause thepositive response of the code following track relays.

l In a centralized traffic controlling system for a stretch of singletrack railroad having signals governing traffic in opposite directionsover the stretch, it is necessary that the manual control f a head-blocksignal governing the entrance of trac at one end of the stretch shallact to prevent the manual control of the head-block signal governing theentrance of traic into the` other end of the stretch. Thus, a furtherobject of the invention is toso organizev the' presentV sys--l tem thatthe code transmission through each track section of the single trackstretch will be dependent upon the code transmission in the precedingtrack section for Vthe corresponding direction of code transmission withthe manual.

control of a head-block signal acting bto cause the stopping of the codetransmission from its end of the stretch. This cessation of codetransmission in each of the track sections for one direction in responseto the manual control of a signal obviously prevents code reception atthe distant end of the stretch and thus holds the opposing signal atstop, and also acts to prevent manual interruption of the codetransmission from such distant end of the stretch. This latter featureis essential so that a manual control for the distant end of the stretchcannot, in any way, interrupt the cleared head-block signal or anycleared intermediate signal if the train has already en- H tered thestretch. Y

Another object of the present'inventionis to automatically control theintermediate signals in a stretch of track between passing sidings insuch a manner that they canbe safely allowed to indicate proceed for thepassage of a train inv either direction through a stretch of singletrack after such train has entered the stretch from an outlying trackswitch located at some intermediate `point in the stretch. y

Another object ofthe present invention is to provide indications at thecontrol oce as to trafc direction established and as to the presence oi'trains in Various portions of track. Y

Other objects, purposes and characteristic features of the presentinvention will be in part obvious from the accompanying drawings and inpartpointed out as the description of the invention progresses. f v

In describing the invention in detail reference will be made to theaccompanying drawings in which those parts having similar features andfunctions are designated throughout the several illustrations by likeletter reference characters `which are generally made distinctive byreason of preceding numerals indicative of the location of the signalwith which such parts are associ--` ated and in which: f

Fig. l illustratesV diagrammatically manual control means at a controlofce for the communication of switch' and signal controls to the variousfield stations, together with means provided at the control ofce forvisually indicating on the control panel thejconditions or' trackoccupancy and traic direction established invariousportions of track; Ya

Figs. 2A through 2D when placedpside byside respectively illustrate themanner in which coded track circuits are applied to the' control of thesignals and to the control of traic direction for this embodimentl ofthe present invention;

Fig. 3 illustrates in detail the manner in which approach locking relaysare controlled for the signals at a particular eld station;

Fig. 4 illustrates the manner in which approach locking is applied inthe power operation of a track switch to provide for its safe operation,together with the control of correspondence relays associated with thattrack switch; l p

Fig. 5 illustrates the manner in which .the various indications areprovided in response to conditions at the respective reld stations;

Fig. 6A through Fig. 6K illustrate diagrammatically the vconditions oftrack circuit code transmission for thevarious track sections. undercertain typicalA conditions `of train Eoperation;

Fig. 7 illustrates diagrammatically 4how beat code; impulses are formedby the combination of 75 and'120 codes inthe form.A of the inventionshown in Figs. 2A-2D. Y Y

Fig. 8 shows the trackway of Figs; 2A and 2B and a portion of theircircuits to illustrate a simplified form of the invention.

Fig. 9 illustrates diagrammatically how beat code impulses are formed bythe combination of 75 and 120 codes in the form of the invention shownin Fig. 8.

The illustrations employed inthe disclosure of thisj embodiment ofthefpresent invention have been arranged to facilitate the disclosure asto the mode of operation and the principles involved rather than for thepurpose of illustrating the construction and arrangement of parts thatwould `Uv bei employed in practice.

1 their contacts are shown in a conventional manner, certain'relaycontacts being shown in written Thus, the relays and circutfornland 'identified as of particular relays by the reference charactersappearing directly A abve"` such contacts.

The symbols (-1-) and are employed to indicate the positive and negativeterminals respectively of suitable batteri-es or other sourcesoffdirect-current, and the'circuits with which those symbols'are .usedalways have current owing in' the same direction. The symbols (B+) and(B) indicate connections to the opposite terminals of. a suitablebattery or other direct current source'whichhas a central orintermediate tap designated asv (CN), and the circuits with whichl thosesymbols are used may have current flowing in one'direction or the otherdependent upon the particular terminal-used in combination .with theintermediatetap '(CN).

'In order to simplify the description of the present invention,reference is made from time totimeA to vfunctions common to al1 .partsof a similar Acharacterby use in the description of letter referencecharacters without their preceding numerals'for the designation ,of suchparts. It is to be 'understood 4that such a reference applies toianyparts designated in the drawings by reference characterszthat aresimilar except for preceding numerals Y. associated therewith.

The trackway for vwhich this embodiment of the present inventionis'provided comprises a main stretch of track divided into several tracksections and having associated therewith passing sidings A and B- (seeFigs. 2A through 2D). The right-hand end of` the passing siding A isconnected tothe main track byra track switch 2W, and the left-hand endof the passing siding B is connectedto the main track by the trackswitch each ofwhich has Acoded track circuits. It is to be understood,-and it will be readily apparent as the description progresses, that thenumber of track sections inthe stretch of track between thepassingsidings A andyB can be increased or decreased in accordancewiththe requirements of practice.

Associated with the righthand end of the passing siding A are manuallycontrolled signals 2A, 2B, .3A and 3B, signals 2A andZB being headblocksignals governing entrance into the stretch of track between the passingsidings, and signals 3A and 3B being entering lsignals for governingtrain movements into the siding section and into the passing sidingrespectively. In a similar manner signals 8A, 8B, 9A and 9B areassociated with the left-hand end of the passing siding B. Intermediatesignals 4, 5, 6 and 1 are included in the stretch of track betweenpassing sidings, signals 4 and y being provided for governing eastboundtraicito ltheright) `andlsignals 5 and 1 being provided for governingwestbound traffic (to the left). w

Although the signals illustrated in this embodiment of the presentvinvention are of the searchlight type such, `for example,:as disclosedin the patent to O. S. Field, No. 2,239,316, dated April 22, 1941, itisl to be understood that other types of signals such as semaphoresignals, position light signals, or signals havingv individual colorlamp units could be employedby slight modication of the circuitsdisclosed in this embodiment of the presentinvention in a manner whichwill readily be recognized by those familiar with the art. Thedistinctive indications provided by the searchlight signals in thisembodimen-t oi the present invention are green indications for clear,yellow indications for caution, and red indications for danger or stop.

Each of the track sections in the stretch of track between the passingsidings Aand B; and each of the siding sections 3T and 8-l IThas a codedtrack circuit which includes a code following track -relay TR and asource of current at each end of the track section. For the purpose ofobtaining the. best operating conditions of vthe code following track'relays" and certain broken-down insulated joint protection, it isdesirable that each track relay TR have a polar structure so arranged asto cause the relay contacts to be biased to a deenergized position fromwhich they can be moved only upon energization of the relay windingswith a particular polarity so that current will flow in a directionindicated by arrows in the windings.- Eachof those track sections alsohasat each end a code transmitting relay CP which is. controlled bysuitably selected coding con-tacts for applyingdriven codes of differentrates to the track rails. For purposes of obtaining-the high'speedoperating characteristics for the relays CP, such relays may have polarstructures corresponding to Athat described above for thev track relays'IR,'but this has not been indicated in the. drawings.

Suitablecode forming devices, or coding contacts, lare provided for therespective signalv locations for forming the, different,code ratesemployed'. `Although it is tobe understood that l motor driven .codersor .other code forming devices could be employedl,fthe codes" are formedin this embodiment of the present invention by code oscillators, orcoding; contacts, which can be of a structure such as isishown,l forexample, in the application of O. S. Field, Ser. No. 369,862, datedDecember 12, 1940. "An oscillator of such nature is capableofiorming butone code, thus requiring'separat'e oscillatorsfor forming the 180, l`andvrT5 codesrespectively; The system is so organized' thatV each signallocation requires an oscillator i800 and either an oscillator IZUC or15C depending'upon its relation to other signal locations. In thisembodiment, the' successive signal locations have oscillators 15C` and|20C provided alternately inV order that the code oscillatorsforthepopposite' ends oreach track section will be normally activeatsubstantially different rates'for purposes tobe' hereinafterconsidered. 'l l Relays H and"`D controlled through the medium ofdecoding transformers'are provided for the ends of the coded trackcircuits in the usual manner, each of the H relays being maintainedsteadily picked upr responsive to the pulsing of the associated codeAfollowing track'.I relay at either code rate, andeachof. the relays Dbeing. picked upr responsive only to the pulsing rof the associated codefollowing relay at a rate.

Each of the iield stations has oiiice controlled relays for use in themanual control of the track switches and signals, a relay RGZ (see Fig.2A) being provided for governing the clearing of signals for eastboundtrafc, a relay LGZ being provided for governing signals for westboundtraffic, a stop relay B being provided for the manual restoration of asignal to stop, a relay WN (see Fig. 4) being provided for governing thepower operation of the track switch to its normal position, and a relayWR. being provided vfor governing the power operation of the trackswitch to its reverse position.

Each of the intermediate track sections has included inits trackcircuitat each end a series relay SR. which follows a code only inresponse to the presence of a trai-n in that track section, and uponfollowing the code causes the' energization of the associated slowacting series repeater relay SRP. At the ends of the stretch of trackbetween passing sidings the relays SRP are used for indication purposes,while the relays SRP at the intermediate signal locations are employedin the control of directional stick relays S, directional stick relay Sbeing provided for each intermediate signal for governing thetransmission of codes in the rear of such signal for the control of thesignal in the rear under conditions involving the passage of followingtrains.

Certain of the signals have associated therewith relays YGP which repeattheir proceed conditions, light-out relays LO, and relaysv RGP forrepeating the stop or danger conditions of the signals.

Having thus considered the control apparatus employed in this embodimentof the present invention, a consideration will now be given to the modeof operation of the system under various typical operating conditionswhich would beencountered in practice.

Operation y General.-Befcre considering in detail the circuitorganization provided in accordance withthe present invention, briefmention will be made as to the general mode of operation of the systemin order to obtain the desired mode of operation without specicreference to the circuits involved.

With reference to Fig. 6A, the normal conditions of track circuitcodetransmission are illustrated, the direction of the arrows indicatingthe direction of track circuit lcode transmission through the respectivetrack sections. From this diagram it will be noted that a '75 codeoscillator located at the field station at the right-hand end of theYpassing..siding-` A governs transmission through the track rails in bothdirections from that point. At theinterniediatev signal location havingsignals 4 and 5, however, 1a 120 oscillator governs transmission throughthe track rails in both directions from that point, and inthis way thecode transmitters for the opposite -ends of each of the track sectionsare normally active as governed by oscillators of substantiallydifferent rates. As a result of the transmitters attempting to transmitatidiierent rates for the opposite ends lof each of the track sections,beat code impulses are transmitted through the track rails in bothdirections to energize the track relays at both ends of each tracksection-in thev manner later explained. y D' In accordance with thespecific embodimentl of theinvention shown, although theV transmissionof a beat code in 'each direction through ea'ch'vof the tracksections-under normal conditions energizes a signalcontrol relay H foreach of the intermediate signals, the intermediatesignals fas well asthe manually controlled signals at the field stationsare at. stop.Thisis true because each Vof fthe interr'riediate signals can be`controlled to a proceed position onlyv if theH relay for governing;the'oppo'sing signal atkthatlocationis deenerg'ized.

V`According to he diagram-of Fig. 6B, conditions are illustrated inwhich ahead-block signal has been cleared for governing passage of aneastbound train into the stretch of track between the passing sidings Aand B. Inasmuch as the signal 2B governs `passage" of a train outof thepassing 'siding A, thev conditions of code transmission inthefsiding'section are vnot changed from their normal conditions, butlthe manual control ofthe signal 2B to its proceed position causes theremoval of the 75 code normally transmitted from left to right inthertrack section 2-'-`5T'. The removal of such code causes atumble-down through the remaining track sections in the stretch betweenpassing sidings to providean interlock for the `head-block signalsgoverning entrance to that stretch of track so that the signal SAHor thesignal 9B cannot be controlled to display a proceed indicationfor anopposing train movement. Such tumble-down also provides an interlock inthe circuits to prevent'the Vremoval of the 120Y code transmitted fromrightxto' left in the track ysectionii--9T, as the removal of such codeby an operator inadvertently "attempting Vto establish'an opposing routewould cause restoration of the signal 2B rtostop in advance of thetrain.

. With reference to Fi'g.v6C, it will be noted that a lmanualfcontrolhas' been communicated from.

the-control oflice for causing the signal 8A to indicate proceed, andsuch control of thatsig'nal has caused the removal of the'beatcode-normally transmitted from right to` left in the siding tracksection Il -llfl` to establish an opposing signalvinterlock forpurposesjust described vwith respect to the'interlock Afor the opposing 4signalsgoverningmovement ofA trains in thestretch of track between vthe passingsidings A land B. y

` ItY will -be noted inthe diagrams of Figs. 6C through 6F that' normalconditions of code transmission are restored for the tracksections inthe rear `of an eastbound train, and the restoration of such conditionsprovides a means for allowing thev settingup of'a route for a followingtrain by the manual control of the head-block signal 2A or the signal2B, such control being effective in the same manner'as if the entirestretch of track between the passingsidings Were unoccupiedbyatrain. y

- In Fig. 6G it is illustrated how the system provides for the back-upmovement of trains in a stretch of track between passingrsidings. as.vis often required, for example, as in the movement of a work train.Under the conditions illustrated it is assumed that an eastbound trainhas proceeded pastthe intermediate signal v(i so as to allow the tracksection lf-'l'l to become unoccupied in the rear ofaV train and thusallow the restoration of the directional stick relay 4S `for the nextsignal `in the rear as illustrated in Fig. 6E. VIf under theseconditions the train desires to., reverse its direction'of movement, thedesired procedure is that the train move across thev rail joints pastthe intermediate `signal -T which would be at s'top under suchconditions and send a flagmanv in the direction of signal 5 to observethe indication of that signal.'4 If it is safe for the train to Vproceed'with its back-up movement, the signal will be atv caution asillustrated in Fig. 6G (if the manually controlled signal 3A or 3B attheright-hand end of passing siding A is at stop). If it isunsafe forthe train to proceed in' its backward movement because of theestablish'ment of a. route for a following eastbound train by thecontrolof signal 2A or 2B, the signal5 will be maintained at stop, andthe flagman will not allow the train to proceed with its backupmovement.v

' With'reference vto Figs.' 6Hthrough 6K it will bey noted that thesystem can be readily adapted to conditions in practice in whichoutlying track switches areprovided at intermediate points between thepassing sidings. With reference to Fig. 6H,'it has been assumed that theeastbound train has entered the outlying switch 5W to a pointV beyond`fouling position and has restored the track switch to its normalposition. Subsequent to the restoration'of that switch, the normalconditions of code transmission in the stretch of track are restored,and the return of the train to the main track as illustrated in Fig. 6Jcauses a tumble-down of the code transmitters in both directions fromthe track section directly associated with the outlying switch. Inaccordance with such' tumble-down,v intermediate signals 5 arid 6 arecontrolled to indicate proceed for train movement in either directionfrom the Vtrack section directly associated with the outlying switch.Such signalswill indicatel clear of caution inY accordance with theconditions of the signalsfin advance. in Fig. 6K, the man'- ual controlof the signali3Al`to ra proceed position allows the transmission of a,driven code from left to right in the track section 2-5'1' to providefork the clearindication of signal 5.,' Normal conditionsl--Under normalbeat code conditions, the code'l` transmitter vrelays CP for theopposite ends of each track 'section are intermittently Y energized bytheir 'associated codin-g l-contacts,` 'but these coding contactsoperate at diierentv code rates, such'a's 75 and 120 times perminute'jso that'current pulses somewhat variablei-in duration andspacing are intermittently transmitted in oppositedirections at dierentintervalsvover the track rails of this track section, and thusintermittently energize the code following track relays TR at both endsof the track sectionat recurrent intervals to'maintain energized anassociated code responsive H relay.

Referring.tother normal beat code conditions for the track sectionZ-ST-,inFigsfZA and 2B astypical of' the othertrack sections, andconsideringzthe preferred organizationv in which a transmitter relay 1CPmay be energized by closure of its coding contacts -only if theassociated track relay TR.` is deenergized, Fig. '7 showsdiagrammatically inthe form of a time chart the relativetiminggintheoper-ation of the coding conof the oscillators 15C and |200 at thesignals 2 andv 5 which .governY rthe lenergization of the transmitterrelays ZCP and SCP respectively, together with the directionv andduration of the'current pulses in the track rails for this track sectionand the resultant energization ofthe track relays ZTR and STR. at theopposite ends of this track section..v In this explanatory diagram yortime. chart of Fig. '7, the vertical lines on thevgraphsv for Ytheoscillator 15C and 120C indicate'opening and closing of the codingcontacts during the lapse of time from left to right, and the combinedvertical and inclined lines in the graphs for the transmitter relay 2CPand CP and the track relays 2TH. and STR indicate energization ordeenergization of these relays, the horizontal lines indicating the timeduration of an unchanged condition in the opening or ,closing of thecoding contacts or energization of the relays. With this explanation ofthe nature of the explanatory diagram of Fig. 7, consideration may nowbe given to the circuits and operation in detail.

With reference to Fig. 2B, the relay v5CP is normally active tointermittently connect the track relay 5TR and the track battery acrossthe rails of the track section 2-5T, such relay being controlled by theContact of the oscillator lZC. Assuming :the relation of the oscillatorsl 20C`and '15C for the opposite ends of the track section 2-5T to be asassumed .for the 'rst impulses in the diagrams of Fig. 7, the relay SCPis ener- -gized for an on period yof the `oscillator' [26C by a circuitextending from (-H, including inormally closed contacts |04 and vH15 ofsignal 5, contact 52 of oscillator lZC, front .Contact 53 of relay 4H,front contact 54 of relay 5H, winding of relay 5CP, and back contact v55of relay 5TH., to The energization of relay 5CP under such conditions isdiagrammatically illustrated in Fig. 7 -by the dotted line 56. Thepicking up of the relay 5CP closes a track circuit for the energizationof the track relay `2TH. at the opposite end of the track sectionextending from the positive terminal of the track battery 51 includingwinding of relay 5SR, front contact :58 of relay .5CP, upper rail oftrack section 2-5T, back contact 59 of relay 2CP (see Fig. 2A), windingof relay 2TR, and lower rail of track -section 2-5T, @to the negativeterminal of track battery 51 (see Fig. 2B) With reference to thediagrams of Fig. 7, the impulse applied to the track circuit by therelay 5CP is terminated by the oscillator IZBC as indicated by thedotted -line 6B. The dropping away of the relay 5CP causes thetermination lof the impulse in the track rails by the .opening of frontcontact 58 (see Fig. 2B), andas a result of the termination of theimpulse, ,the track relay 2TR (see Fig. 2A) is dropped away. `Theclosure of back contactl of relay ZTR causes the energization oftherelay 2CP for the transmission of an impulse from left to right in thetrack section 2-5T as indicated by the dotted line 62 in the diagrams ofFig. 7. Such circuit is closed immediately because of theffon periodformed by the oscillator C. vThe circuit .by which relay 2CP (see Fig.2A) is energized lextends from including contact 63 of oscillator 15C,front contact `611 Vof lrelay Ztl-I, front contact B5 of relay 2-3TR,front contact 4$6 of relay ZAS, Winding of relay ZCP, and back `contactEl of relay ZTR, to

The picking up of lthe relay 2CP opens the circuit for relay 2TH, atback contact v59 ,and closes a circuit for the energization of itherelay ETR extending from thepositive terminal of track battery 61,including the winding yof the relay ZSR, front contact V59 of relayyZCP, upper .rail of track section 2-5'1, back contact L58.of;relay ECP(see Fig. 2B), winding of relay and.

lower rail of track section 2-5T, to the negative terminal of trackbattery El (see Fig. 2A). vIt will be noted from the circuit justdescribed :that the relay 2CP is vmaintained picked upior the durationof the on period of the oscillator 15C,

irrespective of the condition of the oscillator at the opposite end ofthe track section. This is true because the relay ECP for the oppositeend of the track section can be picked up for the transmission of animpulse only after the track relay 5TH. has vbeen dropped away. Thus,the termination of the on period of the oscillator 15C causes thedropping away of the relay 2CP -by the opening of contact 63 ofoscillator 15C as indicated by the dotted line 68 in the diagrams ofFig. 7, and the dropping away of the relay 2CP terminates the trackcircuit code impulse and thus causes the dropping away of the relay 5TH(see Fig. 2B). The closure of back contact -55 of relay ETR closes acircuit by which the relay 5CP can be picked up, because the oscillatorIZUC is at that time providing an on period. Thus', the relay BCP gainscontrol of the track circuit for the transmission of an impulse by theenergization of circuits corresponding to those which have just beendescribed.

Thus, as indicated in the explanatory time chart of Fig. 7, under normalbeat code conditions current pulses are transmitted over the trackYrails of the track section 2-5T in both directions at differentintervals, and hence .the code following track relays 2TR and 5TR at theopposite ends of this track section are both intermittently energized.-In the preferred organization under consideration, these current pulsesare transmitted rst in one direction and then in the opposite directionalternately as many times per minute as the slower 75 code rate, but theduration and spacing of these current pulses ,is variable. This isbecause each transmitter relay 2CP or 5CP is able to apply a `currentpulse to the track rails upon closure of the associated Coding contactsonly after the release of the associated track relay ZTR or STR uponcessation of the current pulse from the opposite end ...of the tracksection. For example, if the vcoding contacts IZOC governing theenergization of the transmitter relay .ECP should close during' Ythe offinterval between the current pulses vfrom the opposite end of the tracksection, then this transmitter relay SCP is at once energized and isalso maintained energized until these coding contacts again open,regardless of the closure of the coding contacts for the .opposite endof the track section, so that the resulting pulse is as long as theregular on period for the 1 20 code rate, as indicated in Fig. 7 for thefirst impulse of the series between the dotted lines 56 and vlill. Onthe other hand, if the coding contacts i200 governing the energizationof the transmitter relay 5CP should close .at a time when the trackrelay 5TR is energized by ya current pulse coming from the opposite endof the ytrack section, this transmitter relay cannot be energized untilsuch pulse ceases; and this results in shortening or sometimes entirelyVblanking out the current pulse for that particular elo,- sure of thecoding contacts |20C, as indicated in Fig. 7 for the second and thirdoperations of the oscillator coding contacts C in the series shown.

In other words, as can be seen by a stud-y of the time chart of Fig. 7,in the preferred organization for creating beat code conditions, ascontrasted in the alternative form vin Figs. 8 and 9 later discussed,the current pulses in opposite directions in `the track rails of thetrack section are not the direct result of the combined operation ofcoding I contact-s operating at .different code rates of 75 and 1,20times per minute; but these current pulses have their durationandifspaccalled a beat cycle.

t'site 'ends of the track section at the same time,

and each track battery isr connected to the 'opposite ends of the tracksection alternately at different intervalsv and with a periodicitycomparable with the slowerV code rate, thereby providing aduration andspacing of current pulses suitable for operating both code followingtrack relays'to `rmaintaina code responsive device energized insubstantially the same manner as inresponse to regularly spaced codeimpulses at the `slower code rate.

The time chart of Fig. 7 merely indicates for purposes of explanationapproximate operating times and conditions for certain selected 75 and120 code rates; andit should'be understood that the'duration and spacingof the current pulses in opposite directions as shown in this Fig. '7'are merely illustrative or typical of the beat code operationcharacterizing this invention. -In this connection, it can be seen thatcoding contacts operating independently at diiferent code rates, such as75 and 120l code rates, will change progressively from a given timerelationship with respect to the on periods until after a predeterminedtime interval, this same time relationship again exists. This timeinterval may be For example, as indicated in Fig. 7, if the codingcontacts operating at 75 and 120 times per minute open at the'sameinstant,'as assumed for Fig. '7, this same relationship recurs after abeat cycle of `4 seconds corresponding with the time required for 5complete code pulses at the 75 rate and 8 complete pulses at the 120rate.

`Inasmuch.V as the oscillators for the opposite ends of a track sectionoperate independently of each other, and may happen to start atdifferent instants or perhaps change their exact code rate, there can beother relative time relationships between the on periods for 'l5 and 120code rates not illustrated in Fig. '7. Generally speaking, Vthe preciseduration and spacing of the current pulses and the length of the beatcycle under the beatcode conditions contemplated, de-

pend 'upon the code rates chosen, the relative timing relation of thecoding contacts, the accuracy with which each oscillator maintains itsparticular code rate, and other factors'; but the parts of the systemcan be readily organized to give under such normal beat code conditionsa duration and periodicity of current pulses in both directions atintervals suitable for the energization of code responsive means at bothends of the track section for the purpose of detecting occupancy andproviding tumble-down control for a system of centralized trafliccontrol for a single track railroad.

At the left-hand end of the track section 2-5T, the pulsing ofcontact 6lof the relay 2TR (see Fig. 2A) causes the track repeater relay 2T? tofollow the beat code 'being received at that end of the track section.It will be noted that the repeater relay ZTP is employed-primarily tolighten the contact load of the track relay ZTR. l' The pulsing ofcontact 69 of relay Z'I'P energizes the primary winding of thetransformer `'lllfn'st indone direction and then the other in an obviouslmanner toinduce `an alternating volt- 'age in the secondary windingsofV that -transformer. The relay 2H energized under 'normal conditionsby current flowing through its winding in a single direction because ofits connection to the center tap of the secondary winding 1| incombination with the use of the rectifying contact l2 of the 'relay 2TP.The relay 2H is sufciently slow acting. to be maintained steadily pickedup when the relay 2TP is active.

At the right-hand end of the track section 2-5T the relay 5H (see Fig.2B) is normally picked up in response to the pulsing of contact 13 ofrelay STP in a manner corresponding to thatwhich has been described forthe energization of the relay 2H, except that energy is applied tocontact 13 of relay STP for the energization of the primary Winding ofthe transformer only in accordance with the closure of back contact 14of the stick relay 4S associated with the intermediate signal 4. Thereason for the inclusion of such contact in the circuit will behereinafter considered.

The inclusion of a back contact of each track relay TR in the circuitfor its associated code transmitting relay CP not only causes morepositive operation of the code following track relays at the oppositeends of a track circuit during the beat code transmission in that trackcircuit, but also provides a check against the energization of theassociated home relays H by foreign currents applied to the track rails.This is because` the application of a steady foreign current (of aparticular polarity if the track relays are polarized as shown) causesthe track relays TR at the opposite ends of the track circuit to besteadily picked up, which, of course, causes their associated homerelays H to drop away and remain deenergized, but this steadyenergization of the track relays could not occur if it were not for theback contacts of such track relays included in the circuits for theirrespective code transmitting relays CP. In other words, the absence ofsuch back contacts would permit the respective transmitting relays CP tocause the coding of theirY own track relays by energy from the foreignsource. This feature of the present inventionis to be considered animprovement over a similar check against foreign currents provided inconnection with inverse codes shown in the prior application of N. D.Preston, Ser. No. 365,- 065, dated November 9, 1940, and no claim ismade herein to any subject matter disclosed in such prior application.

It may be noted that the connections to the track rails vof the trackrelays and battery sources are staggered for adjoining track sections soas to give the usual broken-down joint protection.

Having thus considered the manner in which a beat code normallytransmitted in both direc- -tions through the track section 2-5T iseffective -to cause the relays 2H and 5H to be picked up,

it is to be understood that a similar condition exists under normalconditions for each of the other track sections having a coded trackcircuit, the energization of the H relays for the intermediate signalsbeing eifective only in accordance with the deenergized condition of theopposing stick relays Sas described with respect to the-control of therelay 5H. d

The circuits for the code transmitter relays CP are somewhat differentfor the intermediate signallocations in order to provide the desiredmode of operation for an interlock of the opposing signals. Thus, thecode transmitter relays for cuits arranged to provide a tumble-down ofcode transmission in a particular direction throughout the entirestretch of track lbetween the passi-ng sidings if such tumble-down isinitiated by the rendering inactive of the code transmitter at one endof the stretch of track. Generally speaking, the circuit for the codetransmitter relay CP at an intermediate signal for transmitting codepulses over the track vcircuit in the rear of that signal is governed bythe signal control relay H for the adjacent end ofthe adjoining tracksection in advance of this signal to provide this tumble-down control.More specically, the relay 4CP (see Fig. 2B) is normally active fortransmission of each impulse of a beat code from left to right in thetrack section 4-1T because of the energization during an on"`period ofthe oscillator |20C of a circuit extending from including contacts 50and 5| of the mechanism of signal 4 closed when such mechanism is in itsdanger position, contact 45 of oscillator |200, front contact 16 ofrelay 5H, front contact 11 of relay 4H, winding of relay HCP, and backcontact 18 of relay ATR, to It will be noted from the circuit justdescribed that the dropping away of the relay 5H because of the relayZCP being rendered inactive at the left-hand end of the track section2-5T would cause the relay 4CP to be inactive for the transmission of acode from left to right in the track section 4-1T.

In a similar manner the dropping away of the relay 1H (see Fig. 2C) atthe right-hand end of the track section 4-1T upon the rendering of therelay 4CP inactive would open the circuit for the relay BCP (whichcorresponds to the circuit just described for relay ACP) at frontcontact 19 to stop the transmission of a code from left to right in thetrack section 6--9T.

The control of the code transmitter relays CP for the ends of a sidingsection diiers primarily in that it is the manual control of theassociated signals governing entrance to the sections involved thatrenders the code transmitters inactive. The relay 8CP (see Fig. 2D), forexample, is normally energized for the transmission of each impulse of abeat code by a circuit extending from including contact 80 of oscillator|2|JC, front contact 8| of relayv 8H, front contact 82 of relay 8-9TRfront `contact 83 of relay 8AS, winding of relay 8C?, and back contact84 of relay 8ATR, to It Will be hereinafter pointed out specifically howthe manual control of the signal 8A to a `caution position causes thedropping away of the relay BAS. and the dropping away of such relayrenders the relay BCP inactive for the transmission of a beat codebecause of the opening of front contact 83. The code transmitter relayCP for the vopposite end of the track section 8| IT is controlled in asimilar manner (corresponding to the relay 3GP to Fig. 2A).

The manually controlled signals are all normally at stop and normallydark except for the dwarf signals 2B and 9B governing train movementsout of the passing sidings A and B vrespectively. The intermediatesignals are also normally at danger, and normally dark.

The signal mechanisms for the signals at the iield stations are normallyat stop in accordance with the usual practice in centralized traiiiccontrol systems because of the deenergized condi.- tion of the cnicecontrolled relays LGZ and RGZ associated with the control of themanually controlled signals. The manually controlled .signals that arenormally dark are dark 4because of the joint energization of the Hrelays for the coded track circuits adjacent that iield station, suchcondition being indicative of a normal condition with no routesestablished.

The intermediate signals have their .signal mechanisms normally atdanger because each signal can be cleared only if the H relay for theopposing signal at that location is deenergized. Thus, for example, themechanism of signal 5 :is at stop because the circuit for such signal-is open at back contact of the relay 4H for governing the opposingsignal 4. The lamps of the 4intermediate signals are normally darkbecause of the joint energization of the H relays for the adjacent codedtrack circuits as has been pointed out with respect to the control ofthe lamps for certain of the signals at the field stations.V

Clearing of a head-block signaLJ-Assum'ing the normal conditions toexist as they have lbeen described, and as they are diagrammatical'lyillustrated in Fig. 6A, a typical condition will be described in whichit is assumed that an operator desires to establish a route for thepassage of an eastbound train out of the passingsiding A. Such conditionis illustrated in the diagram of Fig. 6B. Y

To establish such route an operator at the control oiiice actuates thesignal control lever 2-3SGL (see Fig. l) to its right-hand position, andthe closure of contact 86 of such lever in its right-hand positionapplies energy to wire v2 6 for the energization through a codecommunication system or by direct wire of the pick-up winding of therelay ZRGZ (see Fig. 2A). If a code 'communication system is employed,`the lower winding of the relay ZRGZ will have a stick circuit tomaintain such relay4 picked up until it is desired to Icause the signalto be restored to' stop. Such stick circuit can be provided inaccordance with the principles of stick signal control, for example, asshown in my prior application, Ser. No. 365,669, dated November 14,1940. y

The picking up of the relay ZRGZ under-such conditions closes a circuitfor the energizationof the mechanism of signal 2B witha polarityftocause such signal to indicate Acaution (yellow) exftending fromincluding front contact 81 of relay Z-STR, back contact 88 of relay 2D,front contact 89 of relay RGZ, winding of 'signal 2B, front contact 90of relay ZRGZ, front contact 9| of relay ZRCR, back contact 92 `of relayZNCR, front contact 93 of relay 2H, yand back contact 94 of relay 2D, toIt is of course to be understood that the reverse correspondence relayZRCR is picked up for allowing such signal to indicate proceed onlyafter the track switch 2W has been operated to its reverse position. Thetrack switch 2W can be operated to its reverse position in accordancewith the actuation of the switch control lever ZSML (see Fig. 1) to itsright-hand position. The positioning of that lever closes a circuit atcontact 95'of the lever lZSML in its right-hand position to apply energyto wire 28 for causing the picking up of a relay v2WR (not shown) at eldstation No. 2. The control ofthe relay ZWR is provided in a mannersimilar to that illustrated in Fig. 4 for the corresponding relaySWR'associated with the control of the track switch 3W. The picking upof relay 2WR causes the power operation of the track switch 2W 'to itsreverse position, and when it is in its reverse locked position, theassociated correspondence relay ZRCR (corresponding to relay 3 RCR) ispicked up to close the signal control circuit just described.

In accordance with the operation of the mechanism of the signal 2B to aproceed indicating 91.;` 'For the purpose of simplifying thedrawings,

thejcontrol circuit for therelay 2AS is merely indicated-by dotted linesas the circuit for such relay corresponds to the circuit illustrated indetail in Fig. 3 for the corresponding relay SAS associated with theleft-hand end of the passing sid- .ing B.

When the relay ZAS is dropped away in response to the operation of themechanism of signal 21?,r the relay v2CP is rendered inactive for thetransmission of a code in the track section 2--5T bythe opening of frontcontact 66. This initiates a tumble-down which will be effective torender the corresponding code transmitters inactive for therespectivetrack sections included in the stretch ofi track between the passingsidings A and B. f Y.

, At theright-hand end of the track section 25T,V the relays STR (seeFig. 2B) and 5TP become inactive because of the inactivity of the codetransmitter relay 2CP at the opposite end of the track section, and therelay 5H is dropped away. 'I'he dropping .away of relay 5H closesobvious circuits for the energization of the signal lamps of signals 4and 5 at back contact 98, the circuits for the lamps including light-outrelays 4LO and 5LO respectively. w The closure of back contact 99 ofrelay 5H establishes-a circuit for the energization of the mechanism ofsignal 4 with a polarity to cause such signal to indicate caution. Suchcircuit extends from including back contact 99 of relay 5H, backcontact|00 of relay 4D, winding of signal 4, front contact of relay 4H, andback contactI |02 of relay 4D, to The conf ditioning of the mechanism ofsignal 4 to indicate caution establishes a circuit to cause the pickingup of the relay 4YGP extending from including contacts 50 and 5| of themechanism of signal 4, back contact |03 of relay 5SRP, and winding ofrelay AYPG, to The relay 4YGP is suiiiciently slow Ain dropping away tobe main-v tainedpicked up upon the shifting in the position of themechanism of signal 4 to change from a yellow to agreen indication orvice versa.

Conditions are now established whereby the relay 5CPfbecomes active forthe transmission of a 180 code from right to left in the track section2-5T. Such circuit extends from includingcontacts |04 and I 05 ofthemechanism of sig;- nal 5 in its. danger position, contact |06 ofoscillator |800, front contact |01 of relay 4LO, front contactv |08 ofrelay 4YGP, back contact 54 of relay 5H, winding of relay 5CP,'and -backcontact 55 of `relay 5TR,to It will be noted that back contactr55 ofrelay 5TR does not alter the pattern of the 'code transmitted becausethe relay STR remains deenergized.

`At the left-hand end of the track section .'2'L5T,'the pulsingl ofcontact' 69 of relay 2`TP (see -Fig..-2A)A responsive to the 180 codecauses suiiicint energy to flow in the tuned circuit for the relay 2D'tocause that relay to be steadily picked up. Upo'nthe picking up of therelay 2D the shifting of contacts 88 and 94 of such relay in the circuitforjthe control of signal 2B pole changes the winding of such signal inan obvious manner to cause that signal to shift in its position toproevo A cycle of operation withrespect to ytrack circui-t code.transmission'in the track section 4--1T is initiated very similarly tothe cycle of operation which'has been describedwith respect to thetransmission and reception of track circuit codes in the track section2-5'1, such cycle of operation for the track section 4-1Tbeing initiatedwhen the relay 4CP see Fig.. 2B) is rendered inactive for thetransmission of a code upon the dropping away of the relay 5H V.to openits circuit at front contact 16. l n p When vthe relay 4CP becomesinactive for the transmission of a code in track section 4-1T, therelays 1TR (see Fig. 2C) and 1TP at the right-hand end ofthe tracksection become inactive, and the cessation of the pulsing of contact |09of the relay 1'I'P causes the dropping away of the relay 1H. Thedropping away of such relay closes obvious circuits at back contact 0for the `energization of the lamps of signals 6 and`1 and for theenergization of the light-out relay 6LO and 1LO. The mechanism of signal6 isenerg'ized upon the dropping away of the relay 1H with a polarity tocause such signal to indicate caution byY a circuit extending fromincluding back contact of relay 1H, back contact ||2 of relay 6D,winding of signal 6, from contact' ||3 of relay 6H, and back contact |14of relay 6D, to The operation of the mechanism of such signal to a po#sition to indicate caution causes the picking up of the relayv lYGl?y bythe energization of a circuit extending from including contacts ||5 and||6 of the mechanism of signal 6 in its caution position, back contact||1 of relay 1SRP, and windingv of relay'BYGP, to 'I'he pick ing up ofrelay 'EYGB establishes a circuit by which the relay '1CP .becomesactive for the transmission' of a lcode from right to left through theVtrack'rails of trackV section 4-1T. The relay 10P' is lpicked up duringthe on periods of the oscillator |C by the energization of a circuitextending from including contants ||8 and ||9 of signal 1' closedwiththe mechanism oi?Y signal 1 in its danger position, contact 46 ofoscillator |80C, front contactV |2| of relay'BLO, front contact |22 ofrelay GYGP', back contact |23 of relay 1H, winding of relay 1CP, andback contact |24 of relay 1TR, to The reception at the left-hand end ,ofthe track section 4-1T of the 180 code causesl the pulsing of contact|25 of relay 4TP (see Fig. 2B) at a rate to elect the picking up of therelay 4D to pole vchange the circuit for the winding ofsignal 4 by theshifting of contacts |00 and |02, and thereby causev s uch signal todispla a clear (green) indication. i

The relay 6GB (see-Fig 2C) at the left-hand end of the track section6--9T is rendered inactive by the dropping away-of the relay 1H and theopening of its circuit at front contact 19, thus causing the relays9'IR. and STP (see Fig,l 2D) for the right-hand end of the track section6-9T to become inactive. The cessation of the pulsing of contact |26of'relay STP causes the droppingawayfoi the relay 9H, and the droppingaway oisuch relay is effective upon the closure of back contact |21 toenergize 'obvious circuits for the lamps of signals 8A and 9A, suchcircuits including the light-out relays 8LO and 9LO respectively@ l v' yY Inasmuch as itjhas been assumed that no manual control has beencommunicated `to the field station No,l v3 for the clearing of a signalat yide for the displayv or a clear (green) indication. Y7s such v:fieldstation, thev dropping. away of relay 9H is effective only to establisha new circuit by which the relay vQCP is active for the transmission ofa 120 code as selected by the deenergized condition of the relay BYGP.Such circuit extends from including contact |28 of oscillator |20C, backcontact |29 of relay BYGP, back contact |30 of relay 9H, front contact|3| of relay S-Q'IR, front contact |32 of relay SAS, winding of relayBCP, and back contant |33 of relay STR, to It Will be noted that therelay SCP is active to transmit a 120 code without interference undersuch conditions, the code transmitter for the left-hand end of the tracksection 6-0'1 being inactive. The reception of the 120 code at theleft-hand end of the track section 6-9'1' serves to maintain the relay6H picked up and the signal 6 at caution because the relay 6D isresponsive only to a 180 code.

' If an operator has caused the signal 8A at field station No. 3 toindicate proceed, in a manner to be hereinafter considered, the relay8YGP is picked up, and the energized condition of such relay causes thetransmission of a 180 'driven code from right to left in the tracksection 6-9T as indicated in Fig. 6C. Under such `conditions the relayQCP (see Fig. 2D) is active for the transmission of a 180 code by itsenergization for each on period of the oscillator 180C by a circuitextending irom (-1-), including contact |34 of oscillator ISOC, frontcontact |29 of relay 8YGP, back contact |30 of relay 9H, front contact|3| of relay B-STR, front contact |32 of relay SAS, winding of relaySCP, and back contact |33 of relay STR, to

If a 180 driven code is transmitted from right to left in the tracksection 6-9T, the reception of such code at the left-hand end of thetrack section causes the energization of the relay 6D (see Fig. 2C),`and the picking up of that relay pole changes the circuit for theenergization of signal 6 at contacts ||2 and ||4 to cause such vsignalto display a clear indication.

It will be noted that the dro-pping away of the relay 9H at theright-hand end of the track section 6-9T provides an interlock for theopposing signals at the'ends of the stretch of track between the passingsidings to prevent an operator from causing the signal 9A or the signal0B to indicate proceed if he should inadvertently cause the transmissionof a manual control from the control o-filce for the proceed indicationof either of such signals. In the case of the occupancy of the route byan eastbound train. the interlock notonly prevents the proceedindication of an opposing signal, but, in that a proceed indication ofsuch signal is essential in order to render the code transmitter relayCP inactive for the transmission of a code in the track section 6-9T,the interlock insures that the relayA SCP will be continuously active totransmit a code .in the direction of the eastbound train. independent ofany act on tbe part of an o-perator'at the control office with respectto the transmission of controls to eld station No. 3.

Considering the description as it has been set forth for the clearing ofthe head-block signal 2B for governing train movements out of the sidingA, it is believed to be readily apparent to those skilled in the artthat a similar mode of operation is eiective in the control of thesignal 2A associated with train movements from the siding section 3Tinto the stretch of track between the passing sidings A and B. Thus, ifan operator were to cause the clearing of signal 2A, he would operatethe switch control lever 2SML (see Fig. 1)

to its normal position, and would operate the signal control lever2-3SGL to its right-hand position. In accordance therewith, the relayZRGZ would be picked up in a manner which has been described, and theoperation of the track switch 2W to its normal position would cause theenergization of relay 2NCR, if such track switch were not already inthat position. A circuit would be closed under such conditions for theenergization of the mechanism of signal 2A with a polarity to cause suchsignal to indicate caution extending from (-f-), including front contact81 of relay 2-3TR back contact 88 of relay 2D, front contact '8g ofrelay 2RGZ, winding of signal 2A, front contact |35 of relay ZRGZ, backcontact |36 of relay ZRCR, front contact 92 of relay ZNCR, front contact93 of relay 2H, and back contact 94 of relay 2D, to

The opening of contact |31 of the mechanism of signal 2A upon' theoperation of that mechanism to a caution position would cause thedropping away of the relay ZRGP, and the dropping away of such relaywould be eiective to render the relay 2CP inactive in a manner which hasbeen described as being effective in response to the operation of themechanism of signal 2B to a caution position. The rendering inactive ofthe relay 2CP would be eiective to cause a tumbledown of thecorresponding code transmitting means for each of the other tracksections in the stretch of track between the passing sidings A and B,and the application of a code at the right-hand end of the track section2-5T would cause the picking up of the relay 2D to pole change thewinding of signal 2A by the shifting of contacts 88 and 94 to cause suchsignal to be operated to a position to provide a clear indication.

Clearing of entering signaZ.--To consider the control oi a signalgoverning entrance to a siding section, Fig. 2A will be assumed as beingplaced to the right of Fig. 2D, the circuits of Fig. 2A which have beenprovided for the right-hand end of the passing siding A correspondingwith the circuits which are provided but not specifically shown for theright-hand end of the passing siding B.

For consideration of a typical condition with respect to the clearing ofan entering signal, it will be assumed that an operator desires to causethe signal 8A to be cleared for the passage of a train on the main trackinto the siding section 8-| IT, To cause such signal to indicate proceedthe operator actuates the'lever B-SSGL (see Fig. 1) to a right-handposition and closes a circuit at contact |38 to apply energy to wire 34for the communication of a control to the eld station No. 3 forenergizing the relay SRGZ (see Fig. 2D). After such relay is picked up,a stick circuit is established in a manner corresponding to that whichhas been described when considering the control of relay ZRGZ.

The picking up of the relay BRGZ closes a circuit for the energizationof the mechanism of v signal 8A with a polarity to cause such signal toassume its caution position. Such circuit extends from including frontcontact |39 of relay 8-9TR, back contact |40 of relay 8D, front contactIGI of relay SRGZ, winding of signal 8A, front contact |42 of relaySRGZ, back contact |43 of relay 3RCR, front contact |44 of relay 3NCR,front contact |45' of relay 8H, and back contact |46 of relay 8D,.to Itwill be noted that although the signal mechanism `is energized, thesignal is maintained dark unless a route is established in the vrear ofsuch signal as illustrated in Fig'. 6C, or unless thereis a train inapproach of ythat signal; If there were a route established asillustrated in Fig. 6C, the relay 9H would be deenergiz'ed, and theclosure of back contact |21 of such relay` would establish obviouscircuits for the illumination of the lamps of signals.8A,'8B and 9A,"such circuits including'the windings of lightout relays BLOand SLOrespectively.

The dropping away of the relay 8RGP upon the opening rof its circuit atcontact |41 of mechanism of signal 8A causes the dropping away of the'relay -8ALS b'y opening the circuit for such relay at front contact |48(see Fig. 3 for the complete circuit'for' relay 8AS). The dropping awayf When the relay 8CP becomes inactive, the cessationzof the pulsingatthe right-hand end of the siding-section of contact |49 of relay 3TPcauses the dropping away ofthe relay 3H: When the re- Ylay 3H isfdroppedaway, 'the relay 3GP is rendered active to transmit a '15'code (if therelay ZYGP is dropped away). The circuit by which the relay 3GP.isiactivefor the transmission of a 75 code extends from includingcontact |50 of oscil.. lator C,l back contact |5| of relay ZYGP, backcontact |52 of relay 3H, front Contact |53 of relay 2-"3TR, frontcontact |54 of'relay 3AS, winding of relay 3GP, and back contact |55`ofrelay .'3'I'R,` to 'It will be noted that "the code transmitted isa.true '15code rather than a beat code because of the relay 3TR beingsteadily deenergized to maintain the back contact |55 closed. Thereception at the left-hand end of the siding section of the 75 codemaintains the` relay Y0I-l picked up, andV maintains the conditionsvwhich have beenA describedwith respecttov the caution condition of theVsignal 0A.

'If'it'is assumed that an operator proceeds to setp'aroute-foraneastbound train so as to a proceed'position by a circuitextending 'from ;including'contactsV |56 and |31 of signal 2A, frontcontact |51 of. relay ZLO, winding of relay ZYGR-iandbackfc'ontact |58Vof relay 3H, to vIt'will benoted Vthat the inclusion of back con-Ytact`|58 ofrelay 3H in the circuit for the relay ZYGPLchecks that thebeat code normally transmitted fro'nileft to right in the siding'section has been removed before therelay 2YGP is allowed to bey pickedup and to thereby cause an increase in therate' of code transmission inthe rtrack 'section 3T; It willl be noted vthat this increase in rate isaccomplishedby the shifting of contact |5|, of relay ZYGP inthe circuitfor frelaySCP, the closure ofy front contact I 5| of suchrelay applyingenergy through contact |59 :o'f oscillator Y| 80CV to acirc'uit whichhas been described forthe energizationof the relay BCP.

. lWhen a .180 code is transmitted from right to .left in the 'tracksection-8-I IT as illustrated ln Fig;' 6D, the polarity applied to thesignal 8A is V.reversed uponftheshifting of contacts |40 and such B bycontrolling -the signal' 8B to indicate caution,v the operator at thecontrol omce would actuate the switch control lever 3SML to a reverseoperating position to cause the application of venergy to 'the wire 35for causing the power operation of the track switch 3W.

With reference to Fig. 4, theapplication of energy to wire 35 causes thepicking up of the relay SWR by the energization of its upper winding andthe Picking' up of such relay causes the release of relay 3WN by openingits stick circuit at back contact |60, the dropping away of relay 3WNestablishes a stick circuit for relay 3WR, extending from (-1-),including back contact |6| of relay 3WN, front contact |60 of relay 3WR,and lower winding of relay 3WR, to (-)Q In accordance with the pickingup of relay 3WR, a

reverse operatingcircuit for the switch machine f 3SM is closed atVfront contact4 |52, such circuit including normally closed "contacts |63and |64 of the approach locking relays 8AS and SAS respectively. Whenthe track switch has completed its operation to a reverse position, therelay SRCR is picked up by the energization of a circuit extending fromincluding front contact |65 of relay 3WR, back contact |66 of relay 3WN,winding of relay 3RCR, contact |61 of relay 3WP in its left-handposition, and front contact |68 of relay 3WP, to

The relay SRGZ (see Fig.v2D) would be picked up in a manner which hasbeen described if controls were communicated to leld station No. 3 forthe establishment of a route governing train movement into the passingsiding B. The energized condition "of the relay SRGZ, 'with the trackswitch 3W operated to its reverse position, would cause the signal'B tobe energized with a polarity to operate its mechanism to a cautionposition. Such circuit extends from (-1-), including front contact |69of relay 8RGZ,winding of signal 8B, front contactA |10 Vof relay 8RGZ,front contact |1| of relay 3RCR, back contact |12 of relay SNCB, andfront contact |13 of "relay s-9TR,t0 j j It will be noted that althoughthe operation of the mechanism of signal 8B to a caution position wouldcause thedropping away of relay BRGP by the opening of its circuit atcontact |14, and the dropping 'away of relay 8RGP would cause thedropping away of relay 8AS by the opening of its circuit at'frontcontact |48, the code transmitter relay 8CP would not be renderedinactive because of the closure of frontl contact |15 of thecorrespondence relay SRCR to shunt contacts 82 and 83 of relays 8-9 TRand BAS out of the circuit by which the relay 8CP is normally active.Thus,-thle control of signal 8 for the passage of Ya traininto thepassing siding B has no effect upon the beat code normally transmittedin the siding section 8| I'If, therefore allowing the establishment of aroute for an opposing train vthrough the siding section as is oftendesirable upon the meetingof trains.

Passdgeofua train-With reference to Figs. 6B through 6F, 'typicalconditions will be considered with respect to the passage of aneastbound train fromr the passing siding A to the passing siding B. 1

With reference 't`o Figs. 6B and 6C, it will be assumedlthat theeastbound train accepts the head-block signal 2B which has been allowedto clear in a manner which has been described and has entered the endsection 2--5T in the stretch .of track between the passing sidings A andB. Thepassage of the train into the detector trackl section 2-3T causesthe dropping away of the relay 2RGZ (see Fig. 2A) by .the opening of thestick circuit for such relay in accordance with usual practice in thecontrol of stick signals (not shown). It is to be understood, however,that non-stick signals can be used in accordance with the requirementsof practice. The closure of back contact 90 of relay ZRGZ shunts thewinding of signal 2B in an obvious manner to cause such signal to be putto stop. When the signal is restored to stop, the stop repeater relay2RGP is picked up by the energization of a circuit extending fromincluding contacts |56 and |31 of signal 2A in its stop position,co-ntacts 05 andv |16 of signal 2B. in its stop position, and winding ofrelay ZRGP, to The closure of front contact 91 of relay ZRGP with the OStrack section 2-3T occupied by the train establishes a pick-up circuitfor' the relay 2AS corresponding to a pick-up circuit provided undersimilar conditions for the'relay QAS as illustrated in detail in Fig. 3.It will be noted that the picking up of the relay ZASl cannot render therelay 2CP active for the transmission of a code in the track section2-5T while the OS section is occupied because the circuit for such relayis open at front contact 55 of the relay 2-3TR.

When the detector track station 2-3T becomes unoccupied in the rear ofthe eastbound train, the relay 2CP becomes active for the transmissionof a 75 code in the track section 2-5T in the rear of the train asindicated in Fig. 6C. The circuit by which the relay 2CP is active forthe transmission of such code corresponds to that which has beendescribed when considering the normal conditions of the system. It willbe noted that the relay 2CP applies a true 15 code under such conditionsbecause the back contact 6| of relay ZTR is maintained steadily closed.

The presence of the train in the approach of signal 4 causes sucientcurrent to flow in the track circuit for track section 2-5T to renderthe series relay 5SR (see Fig. 2B) active, and in accordance with thepulsing of contact |11 of relay 5SR, the slow acting repeater relay SSRPis picked up and maintained in a picked up po` sition.

The picking up of relay SSRP closes a pick-up circuit for thedirectional .stick relay 4S extendlng from including contacts 50 and 5|of signal 4 in its clear position, front contact |03, of relay BSRP,front contact |18 of relay 4YGP,

and winding of relay 4S, to The picking up of that relay closes a stickcircuit at front contact |19 for shunting front contact |18 of relayllYGP out of the circuit just described. The relay 4YGP is deenergizedupon the picking up of relay ESRP by the opening of back Contact |03,but it is suiciently slow in dropping away to allow time to insure thepicking up of the stick relay 4S. The dropping awai7 of the relay 4YGPopens the pick-up circuit for the relay 4S at iront contact |18, andcloses a stick circuit to maintain the relay 4S picked up extending from(-5-), including back contact |78 of relay lYGP, iront contact |19 ofrelay 4S, and winding of relay 4S, to It will be noted that by thiscircuit organization the stick relay 4S is picked up when an eastboundtrain is in approach of signal 4, rather than being dependent upon astraddle joint type system of energization which is often faulty in itsoperation upon the passage of short trains.

With the relay S picked up and the relay 4YGP dropped away, the relayECP becomes active `for the transmission of a 12,0 code because of theenergization for each onv period of the oscillator |20C of a circuitextending from (-1-), including contacts |04 and |05 of signal 5 in itsdanger position, contact 52 of oscillator |200,

-front contact ofl relay 4S, back contact |08 of relay HYGP, backcontact 54 of relay 5H, winding of relay 5CP, and back Contact 55 ofrelay 5TR, to The transmission of such 120 code in track section 2-5Tconditions the system so that a signal 2A or 2B may be manually clearedfor a following train when the track section 2-5T becomes unoccupied bythe train under consideration. This is true because the normalconditions of beat code transmission becomes ef,- fective in the tracksection 25T when such section becomes unoccupied in the rear of aneastbound train as illustrated in Fig. 6D, thus conditioning the systemso that the signal 2A or 2B can be controlled if desired to establish aroute for a following train. The normal conditions of the codetransmission become effective in the track section 2-5T when suchsection becomes unoccupied in the rear of a train because the codetransmitters for the opposite ends of the track section are both activelat that time.

It will be noted that the relay 4YGP is dropped away in connection withthe control of the stick relay 4S prior to the restoration of signal 4to danger. Such signal is operated to its danger position when theeastbound train enters the track section 4--'|'T, and by shunting suchsection causes the dropping away of relay 4H. The dropping away of thatrelay opens the circuit for signal 4 atl front contact |0I.

When the eastbound train occupies the track `section 4-1T as illustratedin Fig. 6D, and the track section 2-5T has become unoccupied in the rearof the train, although a beat code is transmitted from left to right inthe track section 2-5T, the relay 5H (see Fig. 2C) is maintained droppedaway because of the inclusion in its circuit of back contact 14 of thestick relay 4S. Thus, the opposing intermediate signal 5 is maintainedat danger even though the block in advance thereof is unoccupied by atrain. This is in accordance with the desired mode of operation forgoverning the passage of trains making back-up movements. Such trainmovements will hereinafter be more fully described.

The presence of the eastbound train in the track section 4-1T causes theseries relay 1SR to be active, and to effect the picking up of thedirectional stick relay 5S by the energization ci circuits correspondingto those which have been described in detail with respect to the controlof the relay 4S. The picking up of the relay BS causes the relay 1VCP tobe active for the transmission of a 75 code by the energization of acircuit corresponding to that which has been described by which therelay 5C? has been active for the transmission of a code in accordancewith the energized condition of the relay 4S.

As the eastbound train proceeds further so as to cause the track section4--1'1' to become unoccupied in the rear ofthe train, as illustrated inFig. 6E, the 120 code transmitted from right toleft in the track section4-1T causes the picking up of the relay 5HV (see Fig. 2B). The pickingup of such relay with the relay 4D deenergized closes a circuit for theenergization of the mechanism of signal 4 with a polarity to cause suchsignal to indicate caution. Such circuit extends from (-l-), includingback contact 99 oi

